The primary goals of this proposal are to study the biomechanics of posture at the level of single body segments in relation to age and peripheral sensory deficits in the visual and somatosensory systems that the aging process; also to design and implement effective training programs to improve individual postural stability. There are three specific goals; 1. To quantitatively measure and document the kinematics and kinetics of individual body segments in the young and elderly during balance recovery after an unexpected disturbance at the feet in subjects with various amounts of peripheral sensory deficiency. It is bypothesized that the kinematics and dynamics of individual body segments in response to the external fall-providing stimuli are functions of age and peripheral sensory inputs. 2. To identify and classify the spatial-temporal patterns (STP) of body segmental kinematics and kinetics for successful and failed balance recoveries in healthy and sensory deficient conditions. It is hypothesized that the STP of inter-limb coordination are definable and distinguishable between success and failure of balance recovery, and between healthy and sensory deficient conditions. 3. To design an effective feedback training program to improve the balance recovery ability of fallers. It is hypothesized that feedback training will produce an improvement in the incidence of unsuccessful balance recovery. The kinematic and kinetic variables (i.e. joint angles, moments, linear accelerations at center of mass (COM) of the body segments and the whole body) of eleven body segments i.e. the head, trunk, pelvis, left and right arms, thighs, shanks and feet) will be quantitatively measured during balance recovery after an unexpected disturbance at the feet in the anterior-posterior direction. A total of seventy two subjects ranging from 21 to 76+ years of age will be examined. The measurements will be conducted under various conditions to study the relation between peripheral sensory systems and postural stability. The effect of vision will be studied by opening and closing the eyes and the effect of somatosensory input by testing subjects with peripheral neuropathy who have decreased sensation in their lower extremities. The kinematic measurements will be carried out using the integrated kinematic sensor that was developed by the PI. These measured body segmental kinematics and kinetics will be analyzed to determine their relations to age and peripheral sensory deficiency. In addition, the STP of these kinematic and kinetic variables will be identified. These patterns will be classified based on the recovery success, and will be related to individual age and sensory deficient conditions, using factor and confirmatory factor analysis approaches. Finally, twenty-four out of seventy two subjects will be chosen to participate int he training exercise program. They will be randomly assigned into three groups; training with feedback, training without feedback, and control. The feedback group will receive on-line feedback based on their STP in order to increase the success rate in balance recovery. The STP and athe numbers of failed recoveries will be compared between pre- and post-training, among all three groups. The number of reported fall events will also be compared. This kinematic and kinetic variables (i.e. joint angels, moments, linear accelerations at center of mass (COM) of the body segments and the whole body) of eleven body segments (i.e. the head, trunk, pelvis, left and right arms, thighs, shanks and feet) will be quantitatively measured during balance recovery after an unexpected disturbance at the fee t in the anterior-posterior direction. A total of seventy two subjects ranging from 21 to 76+ years of age will be examined. The measurements will be conducted under various condiitons to study the relation between peripheral sensory systems and postural stability. The effect of vision will be studied by opening and closing the eyes and the effect of somatosensory input by testing subjects with peripheral neuropathy who have decreased sensation in their lower extremities. The kinematic measurements will be carried out using the integrated kinematic sensor that was developed by the PI. These measured body segmental kinematics and kinetics will be analyzed to determine their relations to age and peripheral sensory deficiency. In addition, the STP of these kinematic and kinetic variables will be identified. These patterns will be classified based on the recovery success, and will be related to individual age and sensory deficient conditions, using factor and confirmatory facto analysis approaches. Finally, twenty-four out of seventy two subjects will be chosen to participate int he training exercise program. They will be randomly assigned into three groups; training with feedback, training without feedback,a nd control. The feedback group will receive on-line feedback based on their STP in order to increase the success rate in balance recovery. The STP and the numbers of failed recoveries will be compared between pre- and post-training, among all three groups. The number of reported fall events will also be compared. This study is aimed at trying to close the gap between the basic study of falling mechanisms and the practical task of designing fall prevention training programs so that the age-related falling can not only be understood, but also be prevented. The approach will provide-in-depth information about the functioning of and subtle changes in the postural control system resulting from sensory deterioration during the aging process. It will ultimately be used as the basis for understanding and formulating the postural control theory, and for predicting the individual falling liability. This study is congruent with the national health agenda to apply quantitative techniques to significantly improve the health and well-being of the nations's elderly population over the coming decade.